In air jet weaving looms the above mentioned cutter is arranged on the weft thread insertion side downstream of the main air jet nozzle as viewed in the insertion direction. The cutter is arranged next to the beat-up line for cutting the weft thread when the beat-up motion of the loom slay is completed and when the loom shed has been changed so that the inserted weft thread is securely held in the fabric by the warp threads. The cutting must take place at the very beginning of the return motion of the slay, so that the air insertion channel, specifically the main air jet nozzle is ready for the next weft thread insertion when the loom slay reaches the weft thread insertion position. The proper cutting including the timing of the cutting of the weft thread has presented substantial problems heretofore.
Although scissors type cutters are used conventionally, these cutters cannot properly cut the weft thread if the weft thread is not properly presented for the cutting. For example, proper cutting is not assured if the weft thread extends across the cutting edges with a slant rather than perpendicularly to the cutting edges or if the weft thread does not have the proper tension for the cutting.
In air jet weaving looms the main weft thread inserting nozzle is secured to the loom slay and hence moves along with the loom slay in the beat-up motion. The weft thread passes through the main nozzle coming from a weft thread storage through a thread guide for properly leading the weft thread into the main nozzle. Relay nozzles are arranged alongside the weft thread insertion channel through the reed and these relay nozzles carry the weft thread through the air insertion channel and thus through the loom shed. When the insertion is completed, the slay performs the beat-up motion, whereby the main nozzle travels along with the slay as mentioned, into the position defined by the beat-up line. At this point of time, there is a section of weft thread extending from the fabric edge to the weft thread storage through the main nozzle. The tension on this section of weft thread depends on the instantaneous position of the loom slay and thus of the movement of the main nozzle as the loom slay travels back into the weft thread insertion position. The highest tension in the weft thread is present at the moment of beat-up. The tension slackens again as the slay begins its return movement.
It is desirable to cut the weft thread when it has its optimal tension. For this purpose, the cutter in an air jet loom is mounted in a fixed position next to the beat-up line.
Tests made by the inventor have shown that the cutting of the weft thread also depends on the yarn characteristics or qualities. For many types of yarns the tension present in the weft thread at the beginning of slay return from the beat-up line is insufficient to assure a proper cut. One reason for this difficulty resides in the fact that the thread inside the main nozzle has a tendency to flutter, since the inner diameter of the main nozzle is larger than the thread diameter. The thread nozzle inner diameter is, for example, within the range of 3 to 4 mm. Thus, the air flow through the nozzle can cause the weft thread to flutter. As a result, it was possible heretofore for the weft thread to slide below the cutter and thus not be cut at all.
Even with the weft thread still extending across the cutting blades of the scissors, a proper cut is not assured if the tension is insufficient so that the closing scissors blades just squeeze the weft thread to produce a fuzzy cut, rather than a clean cut. Both thread ends then may have a fuzzy appearance and this is undesirable, especially for the weft thread end that must next be transported through the air insertion channel, because the fuzzy end interferes with a proper weft thread insertion and transportation through the channel.